Automatic extension telephone system.



T. G. MARTIN & F. LUBBERGER. AUIOMATIC EXTENSION TELEPHONE SYSTEM.

APPLICATION HLED DEC. 20, 1906. 1,151,547. Patented Aug. 24, 1915.

5 SHEETS-SHEET I.

1.1;. MARTIN 61 F. LUBBERGER. AUTOMATIC EXTENSION TEU-IPHONE SYSTEM.

APPLICATIGN FILED DEC- 20. I906.

Patented Aug. 24, 1915.

5 SHEETS-SREET 2.

- ram/m rQ 6 zja A72 0?" T. G. MARTIN 81 F. LUBBERGER. AUTOMATIC EXTENSfON TELEPHONE SYSTEM.

APPLICATION FILED DEC. 20. I906- %.a, T. m MMe MN MW pa 0 m fl f m 2%? P Q a? A r 7 a y m WZ 5 1 l l m a a 1 T 1 1 K T G. MARTIN & F. LUBBERGER. AUTOMATIC EXTENSION TELEPHONE svsnm.

APPLICATION FILED DEC. 20, I906.

Patented Aug. 24, 1915.

5 SHEETSSHEET 4.

T. G. MARTiN & F: LUBBERGER.

AUTOMATIC EXTENSION TELEPHONE SYSTEM.

APPLICATION HLED DEC. 20 1906- 1,151,54:7. Patented Aug. 24, 915.

5 SHEETS SHEET 5.

UNITED STATES PATENT OFFICE.

TALBOT o. MARTIN AND FRITZ nunnnnenn, or cmcne nmnsrois, 'n'ss ronons z ir nn-zsnn ASSIGNMENTS, T0 FIBS'I' TRUST AND snvms BANK, of cm- CAGO, ILLINOIS.

LUTOMATIO EXTENSION 'rnnnrnonn srsm.

Specification of Letters P'atent.

Patehted Aug. 24, 19in.

Application filed December 20, 1906. Serial No. 348,752.

T 0 all whom it In ay concern:

Be itknoun that we, TALBOT G. Ham and Fnnz Loom-menu, both citizens of the United States of America, andresidents of Chiaigo, Cook county, Illinois, have inrented a certain new and useful Improvement in Automatic Extension Telephone Systems. of which the following is a specification.

Our invention relates to automatic telephone exchange systems in which a telephone line is provided with a master telephone and one or more extension telephones.

An automatic telephone extension or party line lock-out arrangement is disclosed in application Serial No. 292.188.

An objectof our present invention, which is subordinate to said prior application, is to provide an improved and highly efic'ientlock-out arrangement for the extension lines of an automatic telephone system.

Another object is to provide certain novel fea tures and details of construction and combina'ions which will permit intercoinmunication between the extension subscribers, as well as between the extension subscribers and the main or master telephoneoperator, and which will in 'rariousother ways increase the efiiciencyand improrethe-servioe of a system ofthis'particular character.

To the foregoing and other useful ends, our invention consistsin matters hereinafter set forth and claimed.

In the accompanying drawings, 1 is a top plan view of the look-out switch with the cover removed. Fig. 2 is a side elevation of the switch. Fig. 3 is a; top plan view of a portion of the look-out switch, showing a number of the relays. and also showing the switch. in use. Fig. 4 is an end view of the lock-out sWitch.-with the cover in place. Fin. 5 is a diagram showing the general circuit connect-ions for the accommodation of six party line or extension sub motions Xos 1. 2. 3. 4. 5 and 6. Fig. tishows diagrammatically the lookout switch and one extension telephone A and the master telephone F. Figs 6 and 7 taken together show diagrammatically the substation D connected with a first-selector E. connector C. and first-selector H of the callediline leadin to the 10ck-out switch shown in Fig. of

In Fig. 7 the ringer generator is shown at I and the busy signaling apparatus at J.

The battery B for the. lock-outbox, as

No. 1,101,853. issued June 30. 1914. Thesubstation comprises the usual receiver 2, switch-hook induction-coil 4 consisting of the primary winding 5 and'secondary fw inde ing 6. transmitter 7. local battery Band ringer 9. p 7

In addition to the abovementionedparts the substation is provided with an impulse wheel 10 which has the usual vertical impulse teeth 11, which latter are adapted to operate the vertical spring 12. The impulse wheel carries the rotary impilse tooth 13 h c fip m e e rotary impe spring 14. The switchdiook has radiating from its bodganumber of com armslz', 16 and 1?, and is pivotally secured to thekeyboard (not shown) by the screw 18 about which it moves. The movement is'produoed by a spriiilgfnotflslhown, and tfhe'switch-hook 1s operate or e nrpose o changmg' certain circuit connecti ns to be The camarm 15 controlsthe so-called locking arm 19 that normally rests in the position shown at substation A. After-the dial is rotated the locking arm It) occupies the position shown at substationD, and the cooperating'ground springs 201111121 engage, thus placing the ground post contact with thesubstation ground G Whenthe subscriber releases the dial after rotating it, .as described, the vertical impulse teeth 1 1 Will cause the vertical impulse spring 12 to come into contact with the ground post 22, "and immediately after, the rotary impulse ;t0oth 13 causs the rotary impulse spring 14 to come ineontact with the same ground post;

the 9 across the line. The springs 24 and 25. and 26, and 27 are then disengaged, and the primary circuit, including the winding .5. in series with: the transmitter 7 and localhzittery. Ejis interrupted by the separation of the springs 26 andi 'l'. The disengagement of the springs 24 and :25 removes the secondary winding 6 and the receiver 2 from acro$ the Line. whereby a subscriber .may signal another, after a connection has been established, comprises a push-button 28 and a spring 29. which latter normally engages the contact point but when the push-button 28 is PM. the spring 29 leaves the contact point 30'and engages the contact point 31, which latter is connected with the substation ground G. Means whereby the subscriber may releam the central station apparatus brought into service comprises three springs 32. 33 and 34*known as the release springs, and so'controlled by the cam arm 16 that when the switch-hook descends the three release springs are broughtinto contact. theregrounding both of the subscribers line conductorssimnltaneonsly. Furthermore,the substations-connected with the look-out box,

' ns-shown at A in Fig. 6; for instance. have in addition to the aboyementioned parts the ground closing springs 35 and 36 controlled by the cam arm 37. At each substation A there is also provided a boner 38 by which the operator at the master telephone- F signals a subscriber at the extension telephone.

The first-selector shown at B may be of any suitable or approvedtype, for instance of the general type described in Patent No. 815,321, granted March 13 1906, to Keith. Erickson and Erickson. Amon other details it embodies the following we -known devices and circuits: A switch-shaft (not shown) carries the vertical and rotary wipers 39and 40, rely, and the private wiper 41 and the side-switch, which iswell'known, and which comprises the side switch-wipers 42 43, 44 and 45, known as the vertical, rotary and private side switch wipers'and therotary magnet side switch Wiper, respectively. The side switch is under the control of the private magnet 46,- nnd through the medium of th vertical line relay 47. and while the side is in first position, the subscriber con trols the vertical magnet 48, which latter operates to the shaft and shaft wipers 39, 40 and 41 vertically. By means of the rotin-y line relay 49, and while the side switch is in first or second position, the subscriber controls the private magnet 46 -and,'-there fore thside switch. hile the side switch {is in mud position the rotary magnet 50, which carries the shaft and shaft wipers in a rotary'or c'rrcular'direction. is energized. The vertical and rotary line relays 47 and 49, acting conjointly. provide means whereby the subscriber controls the release magnet 51 The signaling device while the side switch is in the first or second position. After the side switch passes to third position, and since the first-selector is of the trunk-release type, the side switch is controlled through the next switch with which a connection has'been established, by

way ofthe private wiper 41 and by means of the back-release relay 52.

ing current for signaling the subscriber may thenoperate either or both of the relays -27 and 49 and cause some interference with the connection. It is also desirable to remove the bridge formed through the said relays from acres the. line to give the roicecurrents as clear a path as possible. The firstselector switch-shaft is also provided with a normal post arm 5- which, when the shaft isin normal position. closes the spring 55 in contact with the contact point 56; but when the shaft is raised one or more steps the spring 55 closes in contact with the contact point 57. The connector switch C may also be of any suitable or approved type. for instance' of the type described in Patent No. 815.1?6. granted March 13, 1906. to Keith. Erickson and Erickson. The mechanical details of the first-selector and connector. as is well known, are very much the same, althoughithere is some material difference in the circuits. The connector switch-shaft (not shown), like th'efirst-selector switchshaft -carries the line. wipers 58 and 59 and the privateaviper'fifl. The connector switch is also controlled by the calling subscriber throu the medium'of the ertical androtary line relays 61 and625 The vertical line relay'fil directly controls the vertical magnet 63 and also the rotary magnet 64 and ringer relay 65. The ofice of the vertical magnet 6335 to give the shaft and shaft wipers their rertical motion, and the rotary magnet 64 imports to the shaft and shaft wipers a rotary or circular motion. The rotary line relay 62 controls the private magnet 66, which latter under certain conditions in turn controls the vertical and rotary magnets 63 and 64.the release magnet 67'. and also the side switch wipers 68, 69, T0 and 71. The side switch of the connector. like the side switch of the first-selector, has a normal or first position, a second position and a third position. The release magnet 67 is also controlled by the line relays 61 and 62 conjointly. By the condensers 72 and 73 the main line circuit pasing through the con nector is divided into two sections The back-bridge relays 74 and 7 5 give the called subscriber means whereby he may release the connector switch which has been connected with his line. The central ofice is equipped with a busy signaling apparatus J of any suitable design, as, forexample, the one comprising an interrupter 76 in series with the primary winding 77 of the induction-coil 78,*whereby a busy signaling current is induced in the secondary winding?!) of the said coil. The secondary winding 79 is connected to the contact point as shown. The connector switch-shaft also carries a normal post arm 81 which, when the connector shaft is ofl normal, allows the spring 82 to engage the contact point 80, thus closing the busy signaling circuit.

The first-selector H of the cailed line is the same as the first-selector E of the calling line. and. therefore. the description of selee tor E is applicable to selector H.

The substation F is similar to substation D and requires no further description.

The look-out switch herein disclosed is of such a nature thata variety of combinations of connections may be secured between telephones by its use.- In fact, owing to its 1mproved character the same service may be had as by the use of a private branch exchange- For instance, a party line subscriber to the'lock-out switch may call to the main exchange without-any assistance from the master telephone subscriber. He operates his dial in the well-known manner for each digit of the desired number. When the calling subscriber turns the dial for the first digit all other party line subscribers, except the master telephone subscriber, are automatically locked out, and upon replacing the receiver to the switch-hook the lockout switch is resin-red. A ny subscriber al- Iotted to the lock-out switoh'may be placed in communication with any other local suhscribe-r thereto by removing his receiver and pressing the signaling button, thus signaling the master telephone station. The attendant atthe main telephone upon learning which local line station is desired simultaneonsly presses two lock-in buttons, one allotted to the milling sulzustation'and the other to the desired substation, thus lockingin both substations on the same line to the exclusion of all-other local subscribers. The

attendant at the main telephone now presses a signaling button forsignaling the desired substation. Either subszriber, upon restoring receiver to the switch-hook, releases the look-out switch mechanism. Saidiockout, switch is provided with the locking-in relays i3, Si, and 88, oneof which is allotted to each party line or extension telephone connected with the look-out switch, and through the medium of which the allotted subscriber is locked in or oilt by' the lock-in bar hereinafter described. Each loclg-ing elay, therefore, performs'the saine function for its individual line, and what is true of the lock-in relay 83 is true of the relays 84, S5, S6, 87 and 88. The lock-in relay S3, for instance. controls a set of springs 89, 90, 91, 9Q, 93 and 94, a similar set of which is under the control of each lock-in relay. Each relay armature, like the armature 95 of the relay 85. is provided with a semaphore arm 96. which latter is normally maintained with reference to the aperture 97 in the position shown at K. Fig. but when the lock-in relay becomes energized and pulls the armature down, the arm 96 takes the position shown at L, and a visual signal appears at the aperture 97 of the look-out switch cover. The lock-in magnet 98, which energizes together with any one of the lock-in relays, operates the lock-in bar 99 to which reference has already been made. Referring to F ig. 3, suppose the relay 86 to become energized and its armature to shift the springs to the position shown; the lock-in magnet 98 energizes simultaneously and the lock-in bar is operated, looking out the armature 95 of the relay 85-that is, looking it in its normal position, and the armature of relay 86 is locked in its attracted 0r op erated positiom In said Fig. 3, at a, b, and c are shown, respectively, the relative positions of a locking-in relay armature and the lock-in bar lever arm when viewed from the direction indicated by the arrows At a the armature is shown in a lockeclout position-- that is, the armature is locked in its normal positiomas the armature 95 above; at b is shown the armature and lerer arm in normal position, these parts being shown in Fig. 1; at c is shown the lock-in bar lever arm locking the relay armature in its attracted or operated position, as the armature of relay S6 in Fig. 3. When the energizing currentceases to flow through the lock-in magnet 98, the lock-in bar is retained in its operated 'tion by the release armature 100 engagmg the lever arm 101 of the lock in bar. Furthermore, the operation ofthe lock-in bar 99closes the springs 102 and 103 in contact (-Fig. 5), and breaks the engagement of the springs 104 and 105. IOGand 107, and 10S and 109. The release magnet armature 100 is shown in its normal position in Figs. 1 and 5, and in Fig. 3' it is shown in its operated position. The projecting shoulder near the end of the armature has engaged the lever arm 101, while the lock-in bar 99 permits the springs 111 and 112 to disengage. The Said lock-in bar remains in this position. thus locking the armature of relay S6 in its operated position and locking the srmsture of relay 83 in its normal position. The release magnet I13 upon e11 ergizing attracts the armature 100 and draws the shoulder 110 away from the lever arm 101, thus permitting the lock-in bar 99 to resume its normal position.

The lock-in bar 99 is pivotally secured by ill the pivot points 114 and 115, which latter are mounted in the ears 116 and 117, respectively, of the base or mounting frame 118. The lock-in bar 99 is an L-shaped member on one web of which is placed an adjusting screw 119, by means of which the angle through which said bar operates may be regulated. This web also controls the contact springs 102 and 103, 104 and 105, 106 and 10?, and 108 and 109. On the other web of the lock-in bar are mounted the lever arms 120, 121, 122, 123, 124 and 125, which latter when the bar 99 is operated retain the lock-in relay armaturcs in a locked position. The lock-in relays 83, 84, 85. S6. 87 and 88 are rigidly secured to a web 126 formed at a right-angle to the base 118. The release relay 127 is controlled from the substations Nos. 1, 2, 3, 4, 5, and 6 and operatm, when energized, to place the springs 128 and 129 in contact, which springs in turn close an energizing circuit through the release magnet 113, providing the lock-in bar has operated and closed the springs 102 and 103 in contact The differentially-wound buzzer relay 130 is provided, whereby a party line subscribed may, by pressing his signaling button and thus grounding his vertical line conductor, signal the operator at the master telephone when he wishes a connection with the op erator, or when he wishes to be connected with one of the extension subscribers. The subscriber, by grounding his vertical line, oses an ener circuit through the winding 131 of the coil 130 (Fi 5). The armature 132 is attracted, the y opening the contact between the springs 133-and 134, which in turn opens the energizing circuit through the 131; hence the coil becomes deenergized and the armature 132 returns to its normal position, and the springs 133 and 131 again engage, and a the energizing circuit through the win 131 is closed, providing the vertical line is still groimded. The alternate energizafion and denergization of the relay 130 causes the armature 132 to chatter or buzz, which is understood by flie master telephone operator to be his signal In normal position the key 135 maintains the master telephone in connection with the party line telephones, as shown in Fig. 5; but when shifted, as shown in Fig. 6, the master telephone is con nccted to the trunk line that connects the central exchange with the subexchange or lockout switch- The normal position is uxd by the master telephone attendant to communicate with the local subscribers, and the shifted position to connect with the trunk line. A mood key 136 .is provided, whereby the supervising subscriber or operator may, in case of emer 'ency, release an $tablished connection, or while two local subscribers are being connected the key 136 is depressed to prevent interference. To release the lock-out switch mechanism the springs 13? and 138 are forced together to close an energizing circuit through the release magnet 113 when the lock-in bar 99 is in an operated position, and the springs 102 and 103 are in contact; and to. prevent interference the springs 209 and 210 separate, destroying the energizing circuit for each and every lock-in re ay. Furthermore, the look-out switch is equipped with 1ock-in push-buttons 139 and with signaling pushbuttons 140, one of each being provided for each extension line having connection with the look-out switch. If the master telephone receives a call from outside for a connection with substation #1, for example, it becomes necessary to lock the said substation onto the main trunk. This is done by means of the former button 139. This latter is premed once and the supervising subscriber thus energizes the lock-in relay 83 and lockin magnet 98, thereby locking in substation #1 on the main trunk line. The master telephone subscriber, by operating the key 135, as shown in Fig. 6, may bridge his telephone across the line. Of course, the attendant at the master telephone must signal the desired substation #1 by energizing the buzzer 38. This is done by means of the push-button 140 which the supervisory subscriber or operator presses (Fig. 6)- The signal for the substation #1 comes to the lock-out switch, which is suitably equipped with a ringer 141 arranged across the trunk liner The said ringer 14:1, as shown, is connected in series with the condenser 142, andthe said bridging circuit is normally clo edbetween the springs 10 and 105. It will be noticed by referring to Fi 5 and 6 that when the key 135 is thrown, e master telephone is connected with the trunk line through the switch springs 106 and 107, and 108 and 109 that short-circuit the condensers 143 and 144. In order that the master operator may be able to make a call these springs must be in contact. when the outside and inside subscribers are connected, as explained, the said springs are separated, but across the spri 106 and 107, and 108 and 109 are bridged the condensers 143 and 144, respectively; and it will be seen that by the use of the mid condensers the supervisor-y operator may still bridge the master telephone F acrom the trunk line and listen through said condensers, even after the lock-in bar 99 has operated and opened the contact between the springs 106 and 107, and 108 and 109.

From the foregoing it will be evident that a number of substations are afi'orded access to a line of two conductors connected with a central oilice and terminating in a firstselector. such as the first-selector H. Such a line is given one number and any subscriber desiring to communicate with any one of the subscribers of the said line calls in the ordinary wa v'and completes the counection. The signal is received by the oper ator, who inquires which substation is desired and being informed pre$es a signaling button corresponding to the desired substation, said bottom energizing a buzzer at the called substation. The operator at the master telephone then resses the button l39. if substation A is wanted, which locks in subscriber A on the trunk line, and at the same time locks out of service for the time being all of the other extension subscribers telephones. The operation of the lock-out switch may be understood more clearly from its action when an outside subscriber calls to the master telephone subscriber and is given a connection with one of the local subscribers Assume, therefore. that the lockout switch line is "$220 and that the subscriber D at subssation #120 (Fig. 7) wishes to communicate with a subscriber A of the line in quwtion.

The first digit being 2, the subscriber at substation i120 turns his dial for the first digit 2. thereby gromiding the vertical line conductor H5 twice and the rotaryline conductor 1-16 once uponthe return motion of the dial. The, ground post 22 is placed in connection Withthe substation ground G, in a well known manner, by the action ofthe lo" g dog 147. Grounding the vertical line conductor 145 energizes the vertical line relay 4? of'the first-selector. The circuit through the said relay extends from-substation ground G, ground post 22. vertical impulse spring 12;. verticalline conductor 1%, side switch wiper contact point 1-18 to the relay 4'] the bridge-out et 149 and 155210 the battery lead 151,

thence through battery B and to groundfi. Each time the vertical line relay 4:" is energized, the springs 152 and 153 are pressed into engagement and-alien circuitis each time through the vertical magnet 48. The circuit through the said magnet extends from ground G= to "the springs 15-2 and 153, to the private'magnet springs. 15% ancf155, vertical magnet- 48 to the battery lead 151, thence through battery B and to groun b'G- The vertical magnet being operated twice, the first-selector switch-shaft andwipers 39 andj-ilare carried to a level with the contacvpoints' that constitute the terminals of. the trunk line to the connector C. Following the vertical impulms 'the rotary impulse spring comes into contact with the ground post thereby groundingtherotary line conductor 146 once and energizing the rotary linerelay 49 ofthe first-selector once.

The path of the euergizingcurreut may be traced as follows? from. the substation ground'G' to the; rotary line conductor 146;

side switch wiper 43. contact point 156 to the rotary line relay 49. bridge-cut-ofl springs 15?, 149 and 1-30 to the battery lead 151, thence through battery B and to ground G. The rotary line relay 49 upon energizing closes the springs 15S and 152- in contact, thereby closing an energizing circuit through the, private magnet 46 which extends from ground G to the springs 152 and 158. private magnet 1'6 to the battery lead 151, thence through battery B and to ground G. The private magnet 46 being energized for a moment, the side switch of the inst-selector E passes from first to secend position, thereby permitting the side switch wiper 1'5 to engage the contact point 159, thus closing a circuit through the rotary magnet 30. The current-flow is from ground G to the contact point 159, side switch wiper 45, through one coil of the rotary magnet to the interrupter springs 160 and 161, through the winding of the second 7 coil of the rotary magnet 50, thence to the battery lead 151, and through battery B and to ground G. The rotary magnet is energized one step and the shaft wipers 39, 40 and 1 1 are carried into engagement with the bank contacts that. constitute the terminal of the trunk line leading to the connector switch C, assuming that the trunk leading to the said connector leads ofi' from the second-set of contacts of the first level: but if the first trunk line is busy an energizing circarry the wipers past the last busy trunk.

line. However, as soon as the private magnet is denergized the side switch is tripped into third position; but if there are no busy contacts to be pas ed over, as asumed in the first instance, the rotary magnet V 50, as

well known, trips the side switch to. thethird positiomlwith the result that fl1e-side. switch wipers 42, 43, lt-l and i5 engage their respective contact points 162. 163, 1641 and 165, thus extending the subscribers line coudoctors 1-15 and 148 to the connector C.

Also, siucethe side switch wiper engages 1 the ground contact point 161. a guarding potential is established at the private wiper 41 for protecting the seized trunk line frombeing molestedby any other switch.

The second digit called after the sub-,

scriber has connection with the connector C- by way of the trunk-conductors 166 and 167. The subscriber rot-ates the'dial, as described, for the second digit-'2, thereby grounding the vertical and rotary-line conductoxs 145 and 146, which causes the enerr.

oization of the connector vertical and rotary e relays 61 and 62. The current for energizing the vertical relay 61 flows over the following path: from ground G' to the vertical impulse spring 12, vertical hne conductor I45, side switch wiper 42, contact point 162, shaft wiper 39, trunk conductor 166, vertical relay 61 to the battery lead 151, thence through battery B and to ground Each time that the vertical line relay 61 is energized the line relay springs 16S and 169 are pressed into contact, thereby closing an energizing circuit through the vertical magnet 63 over the following path: from ground G to the springs 169 and 168, private magnet springs 170 and 171, s1de switch wiper 71, contact point 172, vertical magnet 63 to the battery lead 151, thence through battery B and to ground G. Each time that the vertical magnet is energized it operates to mix the shaft and shaft wipers one step until said wi are carried two steps to the level in whic is located the terminal of the line #220. When the rotary line conductor 146 is grounded the rotary line relay 62 becomes energized through the follow ng path: from ground G to the rotary 1mpulse spring 14, rotary line conductor 146,

side switch wiper 43, contact point 163, shaft wiper 40, trunk conductor 16?, rotary line relay 62 to the battery lead 151, thence battery B and to ground G. The mergi'zation of the said relay causes the energization of the private magnet 66 over a circuit extending from ground G, springs 169 and 173, private magnet 66 to the battery lead 151, thence through battery B and to ground G, and the release of the side switch from first to second position, thus placing the wipers 68, 69, 70 and 71 in connection with their respective "contact points in the second position. a

The last digit being 0 the subscriber opcrates the dial as previously described, the vertical line conductor 145 ten times and the rotary line conductor 146' once; The vertical and rotary line relays 61 and 61- are 0 ted over previously traced wever, when the line relay springs 168 and 169 engage, a circuit is then closed through the rotary magnet 64 instead of through the vertical magnet 63. The energizing circuit extends from ground G to the springs 169 and 168, private mag net springs 170 and 171, side switch wiper 71, contact point 174, magnet 64 to the battery lead 151, thence through battery B and to ground G. Each time that the et is energlzed' it rotates the shaft and shaft wipers. 58,":79 and 'o'ne step the said wipers are carried into en entiw ith the normal conductors 17 5, 176 andl'i'? that lead to the selector H of the desired Tlie energization of the rotary line relay 62, as previously stated,

completes an energizin circuit through the private magnet 66 whic 1 now operates with one of two results, namely the release of the side switch from the second to third position, or the so-called busy release of the connector, which will be described. Suppose the former result to occur and the side switch to pass to third position, thus placing the side switch wipers 68, 69, 70 and T1 in contact with the respective contact points in the third position. Then when the side switch passes to third position a guarding potential is established for protecting the called line. This potential extends from ground G to the contact point 178, side switch wiper 70 to the shaft wiper 60 which engages the private contact of the called line. The said guarding potential also closes an energizing circuit through the bridgecut-ofl' relay 179 of the first-selector H, thereby removing the brid e formed by the vertical and rotary lice relays of the firstselector H. v

To signal the called subscriber the calling subscriber presses the signaling button 28, placing the spring 29 in contact with the substation ground G, thereby energizing the vertical line relay 61. The path of the energizing circuit extends from ground G, contact point 31, spring '29, springs 24 and 25 to the vertical ine conductor 145, side switch wiper 4:2, contact point 162, firstselector shaft wiper 39, trunk conductor 166, vertical relay 61 to the battery lead 151, thence through battery B and to ground G. It will be remembered that the connector side switch has passed from second to third position, and that the side wiper 71 is in engagement with thelcontact point 180, thereby placing the vertical line relay 61 in control of the ringer relay in the same manner in which the rotary magnet 64 came under the control of the vertical line relay 61 when the side switch passed from first to second position, Therefore, when the vertical line relay 61 presses the springs 168 and 169 into contact the ringer relay 65 is energized by a flow of current from ground G to the relay springs 169 and 168, private magnet springs 170 and 171, side switch wiper 71, contact point 180 to the ringer relay 65 and to the battery lead 151, thence through battery B and to ground G. The ringer relay upon energizing shifts the springs 181 and 182 from the springs 183 and 184 and onto the springs 185 and 185, respectively. This results in separating the calling subscriber's line fIom the called subscribers line and bridging across the line of the latter terminals of the ring:- enerator I. A signaling current is, thereore, sent from the generator I to the ringer 'relay spring 185' and 182, side switch wiper 69, connector shaft wiper 59, normal conductor 176, rotary line conductor 187 to the condenser 142, to the ringer 141, springs 10l and 105 to the vertical line conductor 188, normal conductor 175, connector shaft wiper 58. side switch wiper 68, ringer relay springs 181 and 185 back to the generator I. As soon as the calling subscriber ceases to press the signaling button 28 the ringer relay becomes deenergized and the springs 181 and 182 resume their normal position in contact with the springs 183 and 184. respectively. When the ringer 141 sounds. the supervisor subscriber or operator throws the key 135 to the position indicated in Fig. 6, thus connecting the master telephone to the trunk line over the following path: from the vertical trunk line conductor 186 to the springs 188 and 189, condenmr 1-H. vertical line conductor 190, through the springs 191 and 192, spring 193. winding 19% of the induction-coil 195, through the receiver 196, thence to the rotary line conductor 19? through the condenser 143, springs 19S and 199 to the rotary trunk line conductor 18?. The operator having ascertained from the calling subscriber that the substation #1 is desired now throws the listening key 135 to the normal position. which operation bridges the master telephone across the multiple line terminals of all of the extensionsubstations Among these terminals are the terminals 90 and 93 of the substation #1 which are controlled by the locking relay 83; but substation #1 being desired, the operator now presses the calling button 140, which closes an energizing circuit through the buzzer or bell 38 of the substation #1. The circuit extends from ground G at the buzzer 38 to the conductor 200, push-button springs 201 and 202 to the battery lead 203, [hence through battery B and to ground 9'. When the subscriber A has answered, the operator presses the locking button 139, which closes an energizing circuit through the locking relay $3 and lock-in magnet 98. The energizing circuit is as follows: from ground G" to the push-button springs 204 and 205 conductor 206 to the lock-in relay S3. lock-in magnet 98, springs 207 and 208, springs 209 and 210, release magnet springs 11-2 and 111 to the battery lead 203, and through battery 3 to ground G. The energizat-ion of the lock-in relay 83 causes the desired subscribers line to be disconnected from the master telephone and placed in connection with the trunk line conductors 186 and 187. Thisnew connection is brought about by the shifting of the springs 90 and 93 from in contact with the springs 89 and 92 to engagement with the 91 and 94. Shnultaneous with the cnergizafion of the lock-in relay 83 the lock-in magnet 98 is energized, "and the lock -in bar 99 (Fig 3) is locked in its attnlcted position,

as previously described, which bar 'locks the' armature of the energized relay to hold the extension line in permanent connection for the time being with the main trunk line conductors 186 and 187, and which bar at the same time locks out all armatures of deenergized relays, preventing them from opcrating to establish a connection with said trunk line conductors. After locking in :1 called party on the trunk line the operator may listen-in by throwing the key 135. thus placing the springs 189 and 198 in contact with the springs 18S and 199. However, if it is desired that the operator should not be able to listen-in on conversation over the trunk line. the two condensers 143 and 144 may be disconnected. By referring to Fig. 6. it will be seen that when the condensers 143 and 144 are removed. and the lock-in bar 99 is in a locked position. the master telephone is disconnected from the listening key 135 at the springs 106 and 107, and 10S and 109. The we substations D and A are connected by a circuit extending from the receiver 2 of substation D to the secondary winding 6 of the induction-coil 4, contact point 30, spring 29, springs '2 and 25 to the vertical line conductor 145, side switch wiper -12, shaft wiper 39, trunk conductor 166, condenser 72, ringer relay springs 183 and 181, side switch wiper 6S, shaft wiper 58, normal conductor 17:), vertical trunk line conductor 186, conductor 211. springs 91 and 90 to the vertical conductor springs 213 and 214, and spring 215, through the secondary winding 216, thence to the receirer 217 of substation A, rotary line conductor 218, springs 93 and 94, rotary trunk conductor 219 to the rotary trunk line conductor 187, rotnrv normal conductor 176 and shaft 59,'side switch wiper 69, ringer relay springs 182 and 184, condenmr 73, rotary trunk conductor 16?, shaft wiper 40, side switch wiper 13 and rotary line conductor 146 to the receiver 2 of substation D.

Affect-he conversation has been completed oven the above-traced circuit, the front release occurs when the calling subscriber re stores the receiver '2 to the switch-hook 3, thereby presing into engagement for a moment the release springs 32, 33 and The COfltllCtfOf the said release springs grounds therrtical and rotary line conduct-01s 145 and 1 26 simultaneously from ground G to the release spring 34, thence through the springs 33 and 32 to the vertical and rotary line'onductors, thereby energizing the line relays '61 and 62 of the connector. which carries the springs and -2-24 into contact energizing the relay 52 of the first-selector E in'series with the release magnet 67 of the connector C. The path of the latter circuit extendsfrom ground G to the contact point 16-1, side'switch wiper 44. release relay 52, first-selector switch-shaft wiper 41, con- H'c'tor trunk-release springs 2-23 and 224. re

lease magnet 67 to the battery lead 151, thence through battery B and to ground G. \i'hen the connector release magnet 67 is thus supplied with current it energizes, and as a result the switch-shaft and side switch are restored to normal position, thus breakthe connection between the connector s itch-shaft wipers 58, 59 and and the normal conductors 175, 176 and 177. The baclnrelease relay 52 of the first-selector E being in the same circuit with the release magnet 67' energizes simultaneously with the latter. and presses the springs 225 and 226 into engagement, which in turn closes an energizing circuit through the release magnet 51 of the first-selector E. This circuit extends from ground G through the release springs 2'25 and 226, through the winding of the release magnet 51 to the bat terv lead 151. thence through battery B and to ground G. All of the relays and magnets thus energized attract their respective armatures, and as soon as the substation release springs and 3-! separate and break the ground connection with the line conductors 145 and 146 they again denergize. The calling subscriber thus restores all switching apparatus which he originally brought into use.

The lock-out switch mechanism is restored to normal condition when the called subscriber A hangs up the receiver 217, thus messing the release springs 229, 230 and 231 into engagement. which causes an energizing current to pass through the release relay 127. This energizing circuit extends from grounds G through the winding of the release relay 127, conductor 232 to the release springs 231, 123-1) and 229, where the current divides and passes in two paths, one path extending from the release spring 230 to the vertical line conductor 212, contact sprin 90 and 91. conductor 211, vertical trunk line conductor 186, through the winding of the vertical relay of the selector H, thence through the bridge-cut-ofi springs of the bridge-cut-oil relay new the battery lead 151. thence through battery B and to groundlG. The second path extends from the release spring 229 to the rotary line condoctor 218, springs 93 and 94, conductor 219, rotary trunk line conductor 18?, through the winding of the rotary line relay'lof the selector H to the bridge-ont-ofi springs of the hridgecnt-oil relay l79g'and to'battery lead 151. thence through battery Band to ground G. The energization of the release inlay 12f closes an energizing circuit t ugh the release magnet 113. The release magnet 113 (Fig. 3) upon energizing attracts its armature 100, thus drawing the shoulder 110 away from the lever arm 101 and allowing the lockin bar-99 to resume its normal position. The force which restores the lock-in bar is supplied by; the spring 102, 107, 109 and 105. The release armature 100 upon being attracted closes the springs 111 and 112- in contact, thus restoring the energizing circuits for the locking magnet 98 and the locking relays S3, 84, etc. The armature of the relay 83 being now liberated, the springs 90 and 93 pass out of contact with springs 91 and 9- and into contact with springs S9 and 92, respectively. thus breaking the connection with the trunk line and again establishing connection with the master telephone. restoring the lock-out switch mechanism to its normal position.

The back-release is provided in order that called subscribers may not remain helplesly tied up, so to speak, while the bridgecut-oif relay 179 is energized. Should the called subscriber desire to make an independent call before the calling subscriber releases, he may do so by breasing the established connection and securing control of the first-selector H. The subscriber A, by simply restoring the receiver 217 to the switchhook 220, thus pressing into engagement the release springs 229, 230 and 231, grounds the vertical and rotary trunk line conductom 186 and 1S? simultaneously. As a result an energizing current will pass through the vertical back-bridge relay 7-! and through the rotary back-bridge relay 75 of the connector C. The circuit through the vertical back-bridge relay extends from ground Gr (Fig. 6) through the release relay 127, release conductor 232, release springs 231 and 230 to the vertical line condoctor 212, springs 90 and 91, vertical conductor 211, thence to the vertical trunk line conductor 186, normal conductor 175, connector shaft wiper 58, side switch wiper 6S, ringer relay springs 181 and 183 to the backbridge relay 7-1, to the battery lead 151, thence through battery B and to ground G. The energizing circuit of the back-bridge re lay 75 extends from ground Gr through the release relay 12?, release conductor 232, release springs 231, 230 and 229 to the rotary line conductor. 218, through the springs 93 and 9% and rotary conductor 219, thence to the rotary trunk line conductor 18? and rotary normal conductor 176, connector shaft wiper 59, side switch wiper 69, ringer relay springs 182 and 184, through the winding of the .relay 75 to the battery lead 151, thence to battery B and to ground G. The back-bridge relays 74 and 75, upon energizing simultaneously, press into contact the back-release springs '22? and 228, which completes an energizing circuit to the release magnet 67 from ground G" through the release springs :22? and 228 to the release magnet 64', thence to battery lead 151, and through battery B to ground G. The release 'magnet, is thus energized and the switchshaft wipers 58, 59 and 60 and side are restored to normal position. The

energizing circuit through the bridge-cut-ofl' relav 179 is broken when the shaft wiper 60 leaves the private bank contact; thus the connector switch C is released and the firstselector H is restored to the control of the line #220. By grounding the line conductors 1-15 and 146 the subscriber D may restore the first-selector E. The release of the first-selector E, in this case, is accomplished in the same manner and over the same circuits as explained in connection with the front release. An energizing circuit having been established through the release relay 127. the release of the lock-out switch mechanism occurs, as previously stated. The first-selector H and the lock-out switch now being in normal condition the sub scriber A. desiring to call out on the line, re moves the receiver 217 from the switchhook 2-20, which latter on rising, throu h the medium of the cam arm 37', closes t e springs and 36 in contact. The subscriber A new rotates the dial for the first digit, which act places the cofiperating ground springs 2'21 and 222 in contact, in a well-known manner, thus establishing an energizing circuit through the lock-in relay S3 and the lock-in magnet 98, before the dial begins to return to normal position. This energizing circuit extends from the substation ground G to the ground springs 2'22 and 2221, to the ground springs 35 and 36, to the lock-in conductor'233, through the winding of the relay 83 and winding of the magnet 98, through the springs 207 and 20S, releasing 209 and 210, through the release magnet springs 11-2 and 111 to the battery lead 203, thence through battery B and to ground G. The lock-in relay 83 and lock-1n magnet 98, by reason of the said energizing current, operate with the previously described result, and the vertical and rotary conductors 212 and 218 are shifted to the conductors 211 and 219 which lead to the trunk line conductors 186 and 187. The substation #1 is, therefore, locked-in on the trunk line, and the remaining extension substations are locked out, as previously explained. The subscriber Als line conductors being thus connected to the trunk line, the impulses transmitted by the dial on its return pass out to the lines and to the exchange operating the selector H for the first digit, as the subscriber at D operated the switch E. Of comse, the subscriber, after allowing the dial to rotate to its normal position, operates it again, once for each 5116 ceeding dig't, and thus establishes connection with the desired line in the same manner in which substation D called the line Assume, when the trunk line is thus engaged by a first-selector, that a second subscriber, for example, tries to call to the central oilice; then, since subscriber #2 is locked out, his lock-in relay 84 will not energize; therefore, when he presses the but ton 234, upon attempting to signal, the impulse will operate the buzzer relay 130 of the lock-out switch. The operator, hearing such signal and seeing the semaphore of station #1 in the busy posit-ion, informs the second subscriber that the trunk line is engaged. The current through the buzzer in this case flows from substation ground G through the springs 222 and 221 to the contact 235', spring 215 to the vertical conductor 212, spring 90, contact point 89, winding 131' of the buzzer relay 130 to the contact point 133, armature 134 to the battery lead 203 and through battery B to ground g. When informed that the line is busy the subscriber, of course, hangs up his receiver; but he will,

' in so doing, ground both sides of his line.

In this connection it will be noticed that the buzzer relay 130' is given two windings which are diflerentially related when connected in multiple. Grounding the vertical side of the line when the switch-hook passes down will, therefore, not energize the buzzer, because the rotary side is grounded also, and thus a false signal to'the master telephone is prevented. When the receiver 217 of the first subscriber is restored to the switch-hook 220, after he has made his call, the release of the established connection and the restoration of the lock-out switch mazh anism to its operative condition brought about. It will be understood that in this system when a called line is busy there is established a guarding potential at the connector private bank contacts of the desired line. Therefore, as has alread been suggested, when the calling subscri r grounds his rotary line conductor at the end of the last digit, the connector switch will be released, instead of the side switch passing to third position, as in the case where substation D called #220.

The busy release of the connector C, therefore, follows as a result of the energization of the rotary line relay 62, if the called line #220 is busy, as follows: The said relay 62, upon energizing, energizes the private magnet 66, as previously described, which in turn presses the SPI'iIIg'SL-J' and 228' into contact. As soon as the said springs 227 and 8 engage, the release magnet 67 is then placed in connection with the private wiper 60 (since the side switch wiper 70 is now in second position), which wiper has been previously rotated onto a grounded contact. As a resulta flow of current is sent through the release magnet- 67 from the grounded private wiper to the side switch wiper 70, to the private magnet springs 228 and -227', to the release magnet 64', to battery lead I51, thence through battery B and to ground G. The release magnet 67 upon energizing releases the connector switch-shaft and restores the connector side switch to its first position, returning the vertical magnet 63 to the control of the vertical relay 61. Therefore. if the calling subscriber (Fig. i) presses the signaling button 28 and grounds the vertical line conductor 145. he operates the vertical line relay 61, which latter in turn operates the vertical magnet 63. The vertical magnet armature raises the switch-shaft so that the normal post arm 81 permits the switchshaft spring 82 to come into contact with the spring 80, and the busy signaling current is sent to the calling subscribers station. The calling subscriber, upon hearing the busy signal, will understand that the desired line is in service, and will release the switching appamtus over the same circuits previously described by hanging up his receirer. Suppose now that subscriber #1, for instance, desires connection with substation #5; the former on removing the receiver 217 from the switch-hook 220 is connected with the master substation over the following circuit: from receiver 217 to the rotary line conductor 218, springs 93 and 92, springs 189 and 198, condenser 143, conductor 197, receiver 196, secondary winding 194 of the coil 195 to the push-button spring 193, springs 192 and 191, conductor 190, condenser 144, springs 189 and 198', springs 89 and 90, conductor 212, springs 213 and 211, push-button spring 215, winding 216, thence to the receiver 217. He presses the signaling but-ton 234, which closes an ener circuit through the winding 131 of the buzzer relay 130. The buzzer relay 130 upon energization attracts its armature 132, which causes the springs 133 and 131 to dis engage, thereby brealn'ng the energizing circuit through the winding 131 and denergizing the relay. The relay upon de energizing permits the springs 133 and 131 to again engage, and again complete the energizing circuit through the winding 131. This intermittent energization of the relay 130 continues as long as the spring 215 is held in contact with the point 2-35. The operator at the master telephone upon hear ing the signal removes the receiver 196 and learns that connection with the substation is desired. The master telephone subscriber then simultaneously presses the lock-in push-button 139 of line #1 and the .corresponding button of line #5, thus si' multaneously energizing the locking relays S3 and S7 with the locking magnet 93, and locking the lines #1 and #5 in on the line #920 The energizing circuit for relay :83 extends from ground G through the push-button springs 201 and 205, conductor 206 to the locking relay S3. locking magnet 98, springs '20? and 20S, springs -209 and 210, release magnet springs 112 and 111 to the "=battery lead 203, thence through battery B to ground 51. The relay 8? is energized over a similar circuit. After connecting the lines, as described, the operator presses the signaling button of line #5, which closes an energizing circuit through the hell or buzzer at substation #5. The master telephone subscriber, by operating the key 135, may listen-in to tell when the subscriber at substation #5 answers. The two substations thus locked in on the main line are free from molestation by any local subscriber. except the master telephone subscriber. The master telephone attendant may, of course, if he wishes to insure against any one else seizing the line while the two local lines are being locked, depress the key 136 and break the energizing circuit for the locking magnet 98. Then, after the button 139 of line #1 and the corresponding button of line #5 are depressed, if key 136 is released the relays 83 and 87 are sure to lock-in the connection, as explained; or the operators key may be used in the same way, since the circuit of the locking magnet 98 is controlled by the springs '20? and 208, as shown. When two subscribers are locked in on the main line, provision must be made to prevent a subscriber who is calling from the main exchange from coming in on the said line. This is done by the called local subscriber when he answers the calling local subscriber. That is, the called local subscriber is instructed that upon answering he must prem his signaling button, which groimds the vertical side of his line, as is well known; and since his line is now locked in on the main line, the grounding of thevertical line conductor causes the selectbr shaft allotted to the main line to be raised from normal, whereby the said main line is made busy to all subscribers of the main exchange. Either subscriber #1 or #5, by hanging up his receiver, may release the first-selector and restore the lock-out switch mechanism, as previously explained. since on so doing he grounds both sides of the trunk line in series with the look-out switch release relay 127.

It will be seen that the lock-out switch, as disclosed, afiords means for varied substation connections. When a party desires to call out to the main exchange he removes the receiver from the hook and makes a call in the usual way. The substation is thereby connected to the trunkline, and all other party line substations are automatically locked out. Replacing the receiver releases the connection in the exchange and releases the mechanism of the lookout switch. An incoming call is received by the master substation. but any substation having connection with the lock-out switch may be lockedin on the trunk line and thus receive a call direct. In this case the signaling current would pass through the lock-out switch to the ringer and condenser of the locked-in substation. Connection between any two substations may be made. If it is desired to avoid; the help of an operator for intercommuni'cating'calls, a regular buzzer C11- cuit independent of the look-out switch may be. installed between the different substwations. The relays magnets may be of our suitable resistance, but goodresults have been obtained when the lock in relays 83, S, S6, 87 {mass and the loch-inningnet 98 are wound to a resistance of eight ohms; the windings of the differential" rela;- f to aresistance offive hundred ohms: and the reiease' relay to a resistance of eighteen ohms.

The connectors and the second or third selectors, if any are necessary, canbe arranged on a percentage basis, and can thus be less number than the subscribers. The first-selectbrs can also be employed on a percentage. basis, in any suitable orknown'mann v hi this way aufomatictrunkingisaffo ded between lines on which the extension telephones thereof hare provisions for intercommunicating and for" calling the master telephone. v

What we claim as our invention is:-

1., In a telephone exchange system, the combination of automatic means for trunk-' ing between calling and called: telephone lines, a telephone line provided with a innster telephone and several extension telephones, means'by which the slid automatic trunking means can be controlled from the master telephone or any of extension telephones, means for enabling any extension telephone to call the'mast ertelephone, and means atthemasqer telephone for es; tab'lisliing connection; between any two extension telephones 2. In a telephone exchange system, the combination of antxjmatic means for trunking calling telephonelinosinto connection with called lines, a master telephone, a plurality of extension telepliones,"means controlled atthe telephonesfor calling the masto; telephpne, and meansat eacg of said telep ones or oontrollmg sm automatic trunking means;

31 In a telephone ing between subscribers stations, 2 master telephone, a plurality of extension telephones, means at the master telephone for connecting together any twoextension'tele- I system, the combination of automatic means for trunkfor controlling said automatic trunking means.

5. In a tele hone exchange system, the combination 0 automatic means for trunking between subscribers stations, :1 master telephone, a plurality of extension tele phones, means at the master telephone for c nnecting together any two extension telephones, and means at'the master and extension telephones for controlling said automatic trunking means.

6. In a telephone exchange system. the combination of automatic means for trunking between calling and called telephone lines, a telephone line provided with a master telephone and several extension telephones, means by which the said automatic trunking means can be controlled from the masfor telephone or any of said extension telephones, means for enabling any extension telephonetocall the master telephone. means atthe master telephone for establishing connection between any two extension telephones, and means by which the use of one extension telephone renders all other extension telephones inoperative for l calling.

7. In a telephone exchange system, the

combination of automatic means for trunking calling telephone lines into connection with wlled'lines, a master telephone, a plurality of extension telephones, means controlled at the extensiontelephones for calling the master telephone, means at each of said telephones'for controlling said antomatic trunking means, and means by which the use ofone extension telephone renders all other extension telephones inop erative for calling.

8. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones,-means at the master telephone for connecting together any two extension telephones, means at the extensiontelephones for controlling said automatic trunking means, and means by which the use of one extension telephone renders all other extension telephones inoperative for calling.

9. In a; telephone exchange system, the combination of automatic means for trunking between subscribers stations, :1 master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones. means at the master telephone for controlling said automatic trunking means. and means by which the use of one extension telephone renders all other extension telephones inopcrative for calling.

10. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, :1 master telephone. a plurality of extension telephones, menus at the master telephone for connecting together any two extension te1ephones, means at the master and extension telephones for controlling said automatic trunking means, and means by which the use of, one extension telephone renders all other extension telephones inoperative for calling.

11. In a telephone exchange system, the cmnbination of automatic means for trunking between calling and "called telephone lines, a telephone line provided with a master telephone and several extension telephones means by which the. said automatic trunking'means can be controlled from the master telephone or any ofsaid extension telephones, means for enabling any extensicn telephone to call the master telephone, means atthe'mastertelephone for establishing connection betyrcen any twoextension telephones, and means by :which the use of one extension telephone renders all other extension telephones inopemtixefor receivingcalls- :ev 1 In a telephoneexchange system,,the

combination of automatic means'for trunking calling telephone lines into connection with called lines, a master telephone, a plurality of extension telephones, meansicontrolled at the telephonesfor calling the telephone, at eachvof id .telephmes for, controlling mid automatic trunln'ng means, and means bye-which the use of'one extension telephone renders all other QKtEIISiOILtGlGPhOII-S inoperative for. receiving calls. z

13. In a telephone exchange system, the combination of automatic means for trunk ing between subscribers stations, a master telephone,v a plurality of extension telephones, means at the master telephone for connecting together any two extension tclephones, means at the extension telephones for controlling said automatic trunking means. and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving 14. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any twoextension telephones, means at the master telephone for controlling automatic trunking means, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving calls.

15. In a telephone exchange system, the combination of automatic means for trunking bet-ween subscribers stations, a master telephone, a plurality of extension telephones. means at the master telephone for connecting together any two extension telephones, means at the master and extension telephones for controlling said automatic trunking means, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving calls.

16. In a telephone exchange system, the

combination of automatic connectors for use between calling and called telephone lines, a telephone line provided with a master telephone and several extension telephones, means by which the said automatic connectors can be controlled from the master telephone or any of said extension telephones, means for enabling any extension telephone to call the master telephone, and means at the master telephone for establishing connection between any two extension tele phones.

17. In a telephone exchange system, the combination of automatic connectors between calling and called telephone lines, a master telephone, a plurality of extensioi telephones, means controlled at the extension telephones for calling the master telephone, and means at each of said telephones for controlling said automatic connectors. 1;

18,. In a tele hone exchange system, the combination 0 automatic connectors between subscribers stations, a master telephone, a plurality of extension telephones, means at themaster telephone for connecting together an two extension telephones,

and-means at e extension telephonesifor controlling said automatic connectors 19. In a telephone" exchange system, the combination of automatic connectors between subscribers stafions, a master telephone, a plurality of extension telephones, means at the master telephone for connect ing together any two extension telephones, and means at the master telephone for controlling said automatic connectors.

20. In a tele hone exchange system, the combination of automatic connectors between subscribers stations, 2, master telephone, a plurality of extension telephonm, means at the master, telephone for connecting together any two extension telephones, and means at the master and extension telephones for controlling said automatic connectors.

2L In a telephone exchange system, the combination of automatic connectors between calling and called telephone lines, a telephone line provided with a master telephone and several extension telephones, means by which the said automatic connectors can be controlled from the master telephone or any of said extension telephones, means for enabling any extension telephone to call the master telephone means at the master telephone for establishing connection between any two extension telephones, and means by which the use of one extension telephone renders all other extension telephones inoperative for calling.

22. In a telephone exchange system, the combination of automatic connectors between calland called telephone lines, a master teliefione, a plurality of extension telephones, means controlled at the extension telephones for calling the master telephone, means at each of said telephones for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones inoperative for calling.

23. In a tele hone exchange system, the combination 0 automatic connectors between subscribersstations, a master tele phone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the extension telephones for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones inoperative for calling.

2%, In a telephone exchange system, the combination of automatic connectors between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the master telephone for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones in operative for calling.

25. In a telephone exchange system, the combination of automatic connectors bet een subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connectmg together any two extension telephones, means at the master and extension telephones for controlling said automatic connectors, and means by which theuse of one extension telephone renders all other extension telephones inoperative for calling.

26. In a telephone exchange system, the combination of automatic connectors between calling and called telephone lines, atelephone line provided with a master telephone and several extension telephones, means by which the mid automatic connectois can be controlled from the master telephone or any of said extension telephones, means for enabling any extension telephone to call the master telephone, means at the master telephone for establishing connection between any two extension telephones, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving calls 27. In a telephone efcnange system, the combination ,0? automatic connectors between calling and called telephone lines, a master telephone, a plurality of extension telephones, means controlled at the extension telephones for calling the master telephone, means at each of said telephones for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving calls.

28. In a telephone exchange system, the combination of automatic connectors between subscribers stations, :1 master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the extension telephones for controlling said automatic connectors, and

means by which the use of one extens'on telephone renders all other extension telephones inoperative for receiving calls.

29. In a telephone exchange system, the

combination of automatic connectors be-.

tween subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extenm'on telephones, means at the master telephone for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving 30. In a telephone exchange system, the combination of automatic connectors between subscribers stations, a. mamr telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the master and extension telephones for controlling said automatic connectors, and means by which the use of one extension telephone renders all other extension telephones inoperative for receiving calls.

31. In a telephone system, the combina tion of a line, a master telephone and a plurality of extension telephones on said line, a signaling key-switch for each extension, :1 locking-in key-switch for each extension, automatic means for locking out the extensions not locked-in on the line, a special key-switch for releasing the extensions from the line, and a key-switch for connecting the master telephone with the line.

In a telephone system, the combination of a line, a master telephone and a plurality of extension telephones on said line, a signalingkeyswitch for each extension, a lcclringaln key-switch for each extension, automatic means for looking out the extensions not lockedin on the line, a special keyswitch for releasing the extensions from the line, a key-switch for connecting the master telephone with the line. and automatic means for restoring the lock-out box to normal by the hanging up of an extension telephone.

33. In a telephone exchange system, the combination of automatic means for trunking between calling and called telephone lines, a telephone line provided with a master telephone and several extension telephones, means by which the said automatic trunking means can be controlled from the master telephone or any of said extension telephones, means for enabling any extension telephone to call the master telephone, means atthe master telephone for establishing connection between any two extension telephones, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

34. In a telephone exchange system, the combination of automatic means for trunking calling telephone lines into connection with called lines, a master telephone, a plurality of extension telephones, means controlled at the extension telephones for calling the master telephone, means at each of said telephones for controlling said automatic trunking means, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

35. In a telephone exchange system, the combination of automatic means for trunk ing between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the extension telephones for controlling said automatic trunking means, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

36. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones means at the master telephone for connecting together any two extension telephones, means at the master telephone for controlling said automatic trtmking means, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

37. In a telephone exchange system, the combination of automatic means for trunk ing between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the master and extension telephones for controlling said automatic trunking means, and automatic means for rstoring normal relation between all telephone extensions by the hanging up of an extension telephone.

38;,11], a telephone exchange system, the

combinittion of'automatic means for trunking between calling and called telephone lines, a telephone line provided with a master telephone and several extension telephones, means by which the said automatic trunking means can be controlled from the 7 by the hanging up of an extension telephone,

39. In a telephone exchange system, the combination of automatic means for trunking calling telephone lines into connection with called lines, a master telephone, a plurality of extension telephones, means controlled at the extension telephones for calling the master telephone, means at each of said telephones for controlling said automatic trunking means, means by which the use of one extension telephone renders all other extension telephones inoperative for calling, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

40. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the extension telephones for controlling said automatic trunking means, means by which the use of one extension telephone renders all other extension telephones inoperative for calling, and automatic means for restoring n'ormal relation between all telephone extensions by the hanging up of an extension telephone.

41. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the master telephone for controlling said automatic trunking means, means by which the use of one extension telephone renders all other extension telephones inoperative for calling, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

42. In a telephone exchange system, the combination of automatic means for trunking between subscribers stations, a master telephone, a plurality of extension telephones, means at the master telephone for connecting together any two extension telephones, means at the master and extension telephones for controlling said automatic trunking means means by which the use of one extension telephone renders all other extension telephones inoperative for calling, and automatic means for restoring normal relation between all telephone extensions by the hanging up of an extension telephone.

43. A subscribrs line, a lock-out box, a release relay therefor, and means for grounding both sides of the line through the'eoil of said relay.

14. A subscribers line, a buzzer relay having differential windingsnormally bridged across the line. and means for grounding one side of the line to energize said relay, the differential preventing energizing of the relay when both sides of the line are grounded.

5. A telephone system comprising an extension telephone lock-out box provided with a locking magnet, a circuit for said magnet, another-magnetliaving an armature mechanically controlled by said locking magnet, a key-switch controlling mid circuit; and a second key-switch also controlling said circuit.

-16. An extension telephone system comprising means at the master telephone for supervising all connections between an extension telephone and any other telephone, automatic means for i 0 subscribers into connection with called subscribe-rs. and means at the extension and master telephones for controlling said trunkin means.

7. A telephone system comprising a master telephone. line extensions extending therefroman extension telephone lock-out box provided with relays for connecting the extensions with the main line which main line leads to a central station, and signals operated by said relays. connected with the master telephone.

In a telephone system. the combination of a subscrihers line. a plurality of telephones connected therewith. an electromagneticallv controlled lock out mechanism adapted automaticallv to disconnect all of the telephones from the line except the one in usea source of current for operating said lock-out mechanism. the combination thus set forth including provisions for permining intercommlmimtion between any two of the difi'erent subscribers to whom the line common. :1 mend subscribers line,

and means including automatic switchesfo with Paid {In extending a connection from one line to the other.

49- In an apparatus of the character specified, the combination with a line circuit and a plurality of subscribers station circuits connected in multiple therewith, of means common to all said station circuits and operated fi-om a subscribers station for automatically cutting the remaining station circuits out of the line circuit. and means at a certain one of said stations, which station is provided with a master telephone. for controlling disconnection between any two substations on the same line.

50. In apparatus of the character specified. the combination with a line circuit and a plurality of subscribers station circuits connected in multiple with the line circuit,

of means common to all of said station circuits and operated from a subscriber's station when the circuit is closed through any one of the station circuits for automatically cutting]; the remaining St-ZILIOI] circuits out of the "ne circuit, and means at a certain one of said stations, which station is provided with a master telephone, for controlling (lisconnection between any two substations on the same line.

51. An extension telephone system provided with master and extension telephones, means at one telephone for controlling disconnection between two other telephones on the sarhe line, and an automatic switch for finding the line of said telephones.

52. In an extension telephone system, a master telephone provided with means condisconncct-ion between the extensions thereof, and an automatic switch for finding the line of said telephones 53. In a telephone exchange system, the combination of automatic means for trunking calling telephone lines into connection with called lines. a master telephone. an extension telephone. means controlled at the extension telephone for calling the master telephone. and means at each of said telephones for controlling said aut matic trunl ing. means.

5-1. In a telephone system. the combimh tion of 21 subscribers line. telephones connected therewith. an electrcuiagmeticaH3- controlled lock-out mechanism adapted to automatically disconnect one telephone from the line when the other is in use. a source of current for operating said lock-out mcci nism. the combination thus set forth inclzulinf: provisions for permitting inter-communication between the rliflercnt subscribers to whom the line is common. a second su scz'i er's line. and means including' ant! matic switches for extending a connection from one line to the other.

53. In a telephone system. the comhiuation of a subscrilcr's line. lll(})ilfill onelectromagneticmlNon t|g)llc(l lock-out mechanism associated it one of said telephones and adapted to automatically disconnect one telephonewhen the other is in use, a source of current for operating said lock-out mechanism, the combination thus set forth ineluding provisions for permitting intercommunicat-ion between the different subscribers to whom the line is common. a second sulv 

